超声冲击对7075铝合金残余应力及微观组织的影响

Effect of Constant-current Source Ultrasonic Impact Strengthening on Microstructure and Residual Stress of 7075 Aluminum Alloy

利用ABAQUS软件模拟超声冲击强化过程,分析残余应力场的形成过程及表层残余应力的分布规律;采用单因素试验法,研究超声输出电流和振动系统阻抗阈值两个工艺参数对表层残余应力的影响规律,利用X射线衍射(X-ray diffraction,XRD)残余应力测试仪测量残余应力大小和分析残余应力分布规律,并与有限元分析结果进行对比,验证有限元模拟的合理性。在工具幅值为10μm,频率为28 kHz时,7075铝合金经超声冲击强化后,软件仿真结果:表面形成残余应力层厚度约100μm,最大残余应力值为-574 MPa,出现在表层深度60μm处。试验结果:表面形成残余应力层厚度约120μm,最大残余应力值为-330 MPa,出现在表层深度40μm处,仿真结果数值大于试验结果,但趋势保持一致。恒流源超声冲击强化中,电源输出电流及振动系统阻抗阈值对残余应力的大小和分布均有影响,其阻抗阈值的影响与仿真中幅值的影响更接近;在同样输出电流下,提高阻抗阈值可以在铝合金表层获得较大的残余应力,而阻抗阈值一定的情况,增大输出电流可以在铝合金较深层处获得较大的残余压应力。微观组织分析也直接反映了表面冲击强化的效果。

ABAQUS software was used to simulate the ultrasonic impact strengthening process and analyze the formation process of residual stress field and the distribution regular of residual stress in the surface layer,single factor test was used to study the influence regular of the output current and impedance threshold of the main process parameters on the residual stress.The residual stress size and distribution were measured and analyzed by XRD-ray residual stress tester and compared with the finite element analysis results to verify the rationality of finite element simulation.After ultrasonic impact strengthening of 7075 aluminum alloy by the amplitude of 10μm and the frequency of 28 kHz,software simulation resalts show that the layer of residual stress is about 100μm and the maximum residual stress is-574 MPa at the surface depth of 60μm,which experiment at results show the that:the layer of residual stress is about 120μm and the maximum residual stress is-330 MPa at the surface depth of 40μm.The simulation results are larger than the experimental results,but their trends are the same.In the constant current source ultrasonic impact strengthening,the output current and impedance threshold have influence on the magnitude and distribution of residual stress,and the influence of impedance threshold is closer to the amplitude in simulation.In the same output current,the increase of impedance threshold can obtain large residual stress in the aluminum alloy shallow layer.When the impedance threshold sustain the same value,the larger compressive residual stress can be obtained by increasing the output current.The microstructure analysis is a direct reaction to the surface strengthening.